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12.6 I/O Management
12.6.1 USB Phy Power Down
12.6.2 Video DAC Power Down
12.6.3 DDR Selft-Refresh and Power Down
I/O Management
•
The ARM prepares for power down, typically after an external microcontroller notifies the ARM to
prepare for power down via an interrupt or serial communication.
•
The ARM puts DRR (typically mDDR) in its self-refresh state
•
The ARM writes SLEEPENABLE in system register DEEPSLEEEP to stop the clocks and power down
the oscillators
The Fast NAND Boot mode wake up process works as follows:
•
To wake up from the power down state, an external microcontroller resets the DM355 while driving
GIO0 low.
•
The ROM Boot Loader (RBL) reads the bit GIO0_RESET in register BOOTCFG in the System module
to determine the state of GIO0 during reset. If GIO0_RESET is sampled low during reset, the RBL
executes fast NAND boot mode instead of regular NAND boot mode. Note that Fast NAND Boot mode
requires BTSEL[1:0] to be configured for NAND boot mode.
•
The RBL copies a special fast UBL from NAND to ARM internal memory and then transfer control to
the fast UBL. The fast UBL is responsible for reinitializing the DM355, bringing mDDR out of
self-refresh, and branching to an entry point preserved in mDDR.
Note:
Refer to
for more information on Fast NAND Boot.
You can power-down the USB Phy when it is not in use. The USB Phy is powered-down via the
PHYPWDN bit in the USB_PHY_CTL register of the system control module. USB_PHY_CTL is described
in
. Also, see the TMS320DM355 DMSoC Univeral Serial Bus (USB) Controller Reference Guide
(SPRUED2) for more information.
The DM355’s Video Processing Back End (VPBE) includes one video digital-to-analog converter (DAC) to
drive analog displays, such as NTSC and PAL television displays. The Video Encoder (VENC) module of
the VPBE includes registers for enabling/disabling the DAC. You can use the VIE bit in VMOD to force the
analog output of the DAC to a low level, regardless of the video signal. Furthermore, you can use the
DACCLKEN in register VPSS_CLK_CTRL to disable each DAC clock. See the TMS320DM355 Video
Processing Back End (VPBE) Peripheral Reference Guide (
) for detailed information on DAC
power-down.
The DM355’s DDR controller supports self-refresh and power down. This allows you to put the DDR
device in its self-refresh or power down states for power savings. See the TMS320DM355 DMSoC
DDR2/Mobile DDR (DDR2/mDDR) Memory Controller Reference Guide (
) for detailed
information on DDR self-refresh and power down.
174
Power Management
SPRUFB3 – September 2007